In electron devices, such as electron tubes and ELDs, the hermetic container contains a getter. The getter is heated and activated by illuminating radio waves or laser beams from the outside. Thus, the getter adsorbs gases or moisture within the envelope or emits specific gases. For example, when the electron tube belongs to a vacuum tube, the getter adsorbs gases existing in the envelope, thus increasing the degree of vacuum. When the electron tube belongs to a discharge tube, the getter adsorbs unnecessary gas or harmful gas, other than a discharging gas having xenon or neon as a principal constituent, introduced in the envelope. In the case of ELDs, the getter adsorbs moisture within the hermetic container to prolong the serviceable life.
A fluorescent display tube, in which a conventional getter is mounted, will be explained below by referring to FIGS. 7 and 8. In FIGS. 7 and 8, like numerals are attached to the common constituent elements.
FIG. 7 is a cross-sectional view illustrating a fluorescent display tube in which a conventional ring getter is mounted.
FIG. 7(a) is a cross-sectional view illustrating the portion taken along the line Y2-Y2 in FIG. 7(b). FIG. 7(b) is a cross-sectional view illustrating the portion taken along the line Y1-Y1 in FIG. 7 (a) . Anode electrodes 55, each on which a fluorescent substance is coated, are formed on a glass substrate 511. The mounting member 52 of the holder member (anchor or support) 531 for cathode filaments 532 is formed on a glass substrate 511. A ring container 541, which is filled with a getter material 542, is welded to the getter holder member 543. Grids 56 are disposed between each anode electrode 55 and the filaments 532. Numeral 512 represents a glass front substrate. Each of numerals 513 to 515 represents a glass side plate. Anode wiring conductors, Nesa films on the front substrate, and others are omitted here.
The ring container 541, being an nickel-plated iron envelope, is filled with a getter material 542, made of a mixture of Ba, Ma, or an alloy of them and an additive metal (such as Al or Ni).
In order to activate the ring getter 54, the ring container 541 is heated through the high-frequency induction heating from outside the fluorescent display tube to flush (evaporating) the getter material 542. The particles of the evaporated getter material 542 make a getter mirror film over an inner surface of the front substrate 543.
The ring getter 54, having a special ring container 541 and a special holder member 543, is difficult to be miniaturized and requires a large mounting space. The ring getter container 541 has to be spaced at least 1 mm from the anode substrate 511 because the anode substrate 511 may be cracked during heating. This makes it difficult to miniaturize and thin the fluorescent display tube. Moreover, both the ring container 541 and the holder member 543 lead to higher machining costs. The difficult work for mounting them increases the fabrication cost of the fluorescent display tube.
The mounting place of the ring getter 54 is limited to the metal component such as the mounting member 52. Hence, there is no degree of freedom in the arrangement of the ring getter 54.
In order to improve the drawback of the ring getter shown in FIG. 7, the ring getter shown in FIG. 8, which does not use the special ring container or the special holder member, has been proposed.
Referring to FIG. 8(a), a ring-less getter 54 is formed of an pocket (or a recess), which is filled with a getter material, in the inner surface of the front substrate 512 (refer to Japanese Patent Laid-open Publication No. Tokkai-Hei 5-114373). In this example, the pocket formed in the front substrate 512 leads to the high machining cost. However, the ring-less getter is filled with a necessary amount of getter material enough to provide a getter effect because a deep pocket cannot be made sufficiently.
Referring to FIG. 8(b), using the screen printing or vacuum deposition, the film ring-less getter 54, made of a thick or thick film getter material, is formed in the inner surface of the front substrate 512 (refer to Patent Publication No. WO93/16484). In this example, the thick or thin ring-less getter 54 cannot hold a necessary amount of getter material to provide a sufficient getter effect.
The ring-less getter 54 of FIG. 8(c) may be considered in place of the ring-less getter of FIGS. 8(a) and 8(b). In the ring-less getter 54 shown in FIG. 8(c), the getter material is sintered in the form of a disc of a diameter of 2 mm and a thickness of 0.5 mm. The ring-less getter 54 is attached to the inner surface of the front substrate 512 with the fritted glass 57. In this example, the ring-less getter 54 having a large thickness can hold a sufficient amount of getter material. However, because the adhesive strength, particularly, the adhesive strength between the ring-less getter and the fritted glass, is not strong (the shear strength is less than 1 N), the ring-less getter 54 may be dropped down during the fabrication process of the fluorescent display tube.
Because the getter material deteriorates at high sintering temperatures (for example, BaAl4 is oxidized), the fritted glass for adhesion is sintered at a low sintering temperature (for example, less than 450° C.) in the atmosphere. However, the low sintering temperature causes the residue of an organic constituent (for example, ethyl cellulose) in the fritted glass paste, thus resulting in deterioration of the reliability of the fluorescent display tube. Moreover, in order to flush the ring-less getter 54 with the laser beam, the laser beam reaching the fritted glass 57 releases a large amount of gases, so that the emission of the filament 532 is degraded remarkably.
The present invention is made to solve the above-mentioned problems in the conventional ring getters and the conventional ring-less getters.
An object of the invention is to provide an electron device with a ring-less getter. The ring-less getter has a simple configuration and a degree of freedom in arrangement. Moreover, the ring-less getter is easily mountable and is suitable for miniaturization and thinning of electron devices, such as electron tubes or ELDs. Moreover, the ring-less getter does not cause cracking of a glass substrate due to heating during mounting or during flushing and does not generate gases deteriorating the function of an electron tube.
Moreover, another object of the invention is to provide a method for fixing a ring-getter and a method for activating the same.